Exhaust manifolds have been integrated into cylinder heads to increase the compactness of the engine and to increase exhaust manifold cooling. A cylinder head may be constructed from a single casting to reduce engine construction costs as well as to increase the compactness of the cylinder head. A cylinder head with an integrated exhaust manifold for providing increased cooling of the exhaust system is disclosed in US 2009/0126659. In particular, a two piece water jacket design is provided to increase the cooling of the exhaust manifold in the cylinder head.
However, the inventors herein have recognized various shortcomings with the exhaust manifold disclosed in US 2009/0126659. For example, the cross-sectional area of the engine's inner cylinder exhaust runners may increase losses within the exhaust manifold, thereby decreasing the amount of energy delivered to a turbine positioned downstream of the exhaust manifold. Consequently, the engine's efficiency can be reduced. Furthermore, the cross-sectional area of the engine's two outer cylinder exhaust runners may cause boundary layers within the exhaust manifold that limit exhaust flow from the two outer cylinders. Thus, the exhaust runners of the outer cylinders can further limit engine performance and fuel economy.
As such, various example systems and approaches are described herein. In one example, a cylinder head of an engine with an integrated exhaust manifold is provided. The cylinder head including a first exhaust runner for a cylinder positioned between two other cylinders, the first exhaust runner having a cross-sectional area less than a first area at a location between a first valve guide entry point and a first confluence area for mixing exhaust gases with a different cylinder. The cylinder head further including a second exhaust runner for a cylinder positioned at an end of a cylinder bank, the second exhaust runner having a cross-sectional area greater than the first area at a location between a second valve guide entry point and a second confluence area for mixing exhaust gases from a different cylinder.
By reducing the cross-sectional area of a first exhaust runner, exhaust gases can be concentrated to the center of the exhaust outlet of the exhaust manifold. As a result, impingement of exhaust gases on the exhaust outlet can be reduced to lower losses within the exhaust manifold. In this way, the energy within the exhaust gases provided to a turbine of a turbocharger positioned downstream of the exhaust manifold may be increased, thereby increasing the speed of the turbine.
Additionally, a cross-sectional area and lead-in angle of a second exhaust runner at the end of the cylinder head can be constructed to control boundary layers in the exhaust manifold. The lead-in angle defines an intersection between a line parallel to an outer edge of a straight portion of the second exhaust runner and a plane spanning an exhaust outlet. The impingement of the exhaust gases on the exhaust manifold walls may be reduced to control boundary layers in the exhaust manifold when the lead-in angle is within a particular range. As such, losses within the exhaust manifold may be further reduced.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.